Method for the production of bisepoxides and dithiols

ABSTRACT

Process for the preparation of bisepoxides, wherein a conjugated diene of the formula I 
     
       
         
         
             
             
         
       
     
     where
     R 1  is selected from hydrogen and C 1 -C 12 -alkyl, unsubstituted or substituted by one or more S—H or O—H groups,
       is reacted in the presence of a catalyst which is obtainable by bringing   at least one manganese compound selected from A 2 MnX 4 , AMnX 3 , MnY, MnX 2  and MnX 3  into contact   with at least one ligand L of the formula II   
       

     
       
         
         
             
             
         
       
     
     where
     X are identical or different and are selected from monovalent anions,   Y is a divalent anion,   A is selected from alkali metal and ammonium, which may be alkylated,   R 2  are identical or different and are selected from C 1 -C 20 -alkyl,
 
and at least one coligand which is derived from monocarboxylic acids, dibasic or polybasic carboxylic acids or diamines,
 
with at least one peroxide, up to 4 equivalents of peroxide being used per equivalent of C—C double bond.

The present invention relates to a process for the preparation ofbisepoxides, wherein a conjugated diene of the formula I

where

-   R¹ is selected from hydrogen and C₁-C₁₂-alkyl, unsubstituted or    substituted by one or more S—H or O—H groups,    -   is reacted in the presence of a catalyst which is obtainable by        bringing    -   at least one manganese compound selected from A₂MnX₄, AMnX₃,        MnY, MnX₂ and MnX₃ into contact    -   with at least one ligand L of the formula II

where

-   X are identical or different and are selected from monovalent    anions,-   Y is a divalent anion,-   A is selected from alkali metal and ammonium, which may be    alkylated, and-   R² are different or preferably identical and are selected from    C₁-C₂₀-alkyl and at least one coligand which is derived from    monocarboxylic acids, dibasic or polybasic carboxylic acids or    diamines,    with at least one peroxide, up to 4 equivalents of peroxide being    used per equivalent of C—C double bond.

Dithiols are extremely versatile reagents. Thus, it is known that1,4-dimercaptobutanediol can be used in the purification andstabilization of enzymes (protective reagents for —SH groups, W. W.Cleland, Biochemistry, 3 (1964), 480). Furthermore, DE 22 09 458discloses that so-called 1,4-dithiol-2,3-butanediol and its metal saltscan be used as hair waving compositions and unhairing compositions. DE23 37 101 discloses that n-butane-2,3-diol-1,4-dithiol and its alkalimetal salts can be used for producing permanent waves. DE 21 31 630discloses that compositions comprising at least 0.25% by weight ofdimercaptobutanediol and from about 0.01 to 40% by weight of awater-soluble guanidine compound and having a pH of less than 12 can beapplied to guinea pigs in order to unhair them or to human horny skin inorder to eliminate calluses without resulting in skin irritations inguinea pigs or even erythremia (malignant proliferations of theformation system of the red blood corpuscles). The epidermis remainsintact in the treatment described in DE 21 31 630.

It is therefore desirable to find a synthesis route by means of whichn-butane-2,3-diol-1,4-dithiol and derivatives can be obtained with goodyield and in good purity.

DE 22 09 458 and DE 23 37 101 disclose that racemic dithiolbutanediol,contaminated with slight amounts of dithioerythrol, can be prepared byreacting butadienebisepoxide with hydrogen sulfide in the presence of analkaline catalyst in the range from 15 to 40° C. in a composition whichdissolves hydrogen sulfide and whose volume is in the ratio of at least5:1 to the volume of butadienebisepoxide, and isolating thedithiolbutanediol thus obtainable.

U.S. Pat. No. 5,329,024 discloses that olefins can be reacted in thepresence of manganese complexes with the aid of large molar excesses ofH₂O₂, for example olefin: H₂O₂=1:100) to give epoxides.

D. de Vos et al., Tetrahedron Lett. 39 (1998), 3221 disclose thatbisepoxides of isoprene and of 4-vinylcyclohexene can be prepared byreacting the relevant dienes with a large excess (molar ratio about12:1) of H₂O₂ in the presence of a manganese complex. In spite of thelarge excesses of H₂O₂, however, considerable amounts of monoepoxidesare obtained. Furthermore, the yield of desired bisepoxide is stillcapable of improvement.

It is an object of the present invention to provide a process for thepreparation of bisepoxides and dithiols in good yield and sufficientpurity. It is a further object of the present invention to provide novelmixtures of dithiols and uses for mixtures of dithiols.

We have found that these objects are achieved by the process defined atthe outset.

According to the invention, a conjugated diene of the formula I

whereR¹ is selected from

-   -   C₁-C₁₂-alkyl, such as methyl, ethyl, n-propyl, isopropyl,        n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl,        sec-pentyl, neopentyl, 1,2-dimethylpropyl, isoamyl, n-hexyl,        isohexyl, sec-hexyl or n-decyl, particularly preferably        C₁-C₄-alkyl, such as methyl, ethyl, n-propyl, isopropyl,        n-butyl, isobutyl, sec-butyl and tert-butyl;    -   C₁-C₁₂-alkyl, substituted by one or more hydroxyl or thiol        groups, such as hydroxymethyl, 2-hydroxyethyl,        1,2-dihydroxyethyl, 3-hydroxy-n-propyl, 2-hydroxyisopropyl,        ω-hydroxy-n-butyl, ω-hydroxy-n-decyl, HS—CH₂—; HS—(CH₂)₂— or        HS—(CH₂)₃—,    -   and very particularly preferably hydrogen,        is reacted.

Of course, mixtures of olefins or dienes which comprise conjugated dieneof the formula I can also be reacted.

According to the invention, the reaction is effected in the presence ofa catalyst which is obtainable

by bringing at least one manganese compound, selected from A₂MnX₄,AMnX₃, MnY, MnX₂ and MnX₃, into contact

with at least one ligand L of the formula II

and at least one coligand, which is derived from monocarboxylic acids,dibasic or polybasic carboxylic acids or diamines,where

-   X are different or identical and are selected from monovalent    anions, R³O⁻, F⁻, Cl⁻, Br⁻, I⁻, NCS⁻, N₃ ⁻, I₃ ⁻, R³COO⁻, R³SO₃ ⁻,    R³SO₄ ⁻, OH⁻, CN⁻, OCN⁻, NO₃ ⁻, ClO₄ ⁻, PF₆ ⁻, BPh₄ ⁻, where Ph is    phenyl and F₃CSO₃ ⁻. Cl⁻ and acetate are particularly preferred.-   Y is a divalent anion, particularly preferably SO₄ ²⁻ and HPO₄ ²⁻.-   A are different or preferably identical and are selected from alkali    metal cations, for example Li⁺, Na⁺, K⁺, Rb⁺ and Cs⁺, in particular    Na⁺ and K⁺    -   and ammonium NH₄ ⁺, which may be alkylated, for example        N(R⁴)(R⁵)(R⁶)(R⁷)⁺, where R⁴ to R⁷ are in each case identical or        different and are selected from hydrogen, benzyl, C₁-C₁₂-alkyl,        such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl,        sec-butyl, tert-butyl, n-pentyl, isopentyl, sec-pentyl,        neopentyl, 1,2-dimethylpropyl, isoamyl, n-hexyl, isohexyl,        sec-hexyl or n-decyl, particularly preferably C₁-C₄-alkyl, such        as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl,        sec-butyl and tert-butyl, phenyl or CH₂—CH₂—OH. Examples are        tetramethylammonium, tetraethylammonium, methyldiethanolammonium        and n-butyldiethanolammonium.

R² are different or preferably identical and are selected from branchedor preferably straight-chain C₁-C₂₀-alkyl, for example methyl, ethyl,n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl,isopentyl, sec-pentyl, neopentyl, 1,2-dimethylpropyl, isoamyl, n-hexyl,isohexyl, sec-hexyl, n-octyl, n-decyl, n-dodecyl, n-tetradecyl,n-hexadecyl, n-octadecyl and n-eicosyl, preferably straight-chainC₁-C₁₂-alkyl, such as methyl, ethyl, n-propyl, n-butyl, n-pentyl,n-hexyl, n-heptyl, n-octyl, n-decyl or n-dodecyl, particularlypreferably C₁-C₄-alkyl, such as methyl, ethyl, n-propyl, n-butyl, andvery particularly preferably methyl.

-   R³ is preferably-   C₁-C₂₀-alkyl, for example methyl, ethyl, n-propyl, isopropyl,    n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl,    sec-pentyl, neopentyl, 1,2-dimethylpropyl, isoamyl, n-hexyl,    isohexyl, sec-hexyl, n-octyl, n-decyl, n-dodecyl, n-tetradecyl,    n-hexadecyl, n-octadecyl and n-eicosyl, preferably straight-chain    C₁-C₁₂-alkyl, such as methyl, ethyl, n-propyl, n-butyl, n-pentyl,    n-hexyl, n-heptyl, n-octyl, n-decyl or n-dodecyl, particularly    preferably C₁-C₄-alkyl, such as methyl, ethyl, n-propyl, n-butyl and    very particularly preferably methyl,-   substituted C₁-C₂₀-alkyl, for example (o-cyclohexylpropyl,    2-cyclohexylethyl;-   C₃-C₁₂-cycloalkyl, for example cyclopropyl, cyclobutyl, cyclopentyl,    cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl, cyclodecyl,    cycloundecyl and cyclododecyl, preferably cyclopentyl, cyclohexyl    and cycloheptyl,-   C₆-C₁₄-aryl, for example phenyl, 1-naphthyl, 2-naphthyl, 1-anthryl,    2-anthryl, 9-anthryl, 1-phenanthryl, 2-phenanthryl, 3-phenanthryl,    4-phenanthryl and 9-phenanthryl, preferably phenyl, 1-naphthyl and    2-naphthyl, particularly preferably phenyl    or benzyl.

Particularly preferred examples of manganese compounds used according tothe invention are manganese(II) sulfate, manganese(II) acetate,manganese(II) chloride, manganese(II) perchlorate or potassiumhexachloromanganate(IV) K₂MnCl₆.

It is possible for manganese compounds used according to the inventionto have water of crystallization and/or water of hydration, for exampleMn(OAc)₂.4H₂O, MnSO₄.H₂O, Mn(ClO₄)₂.6H₂O, MnCl₂.4H₂O.

In an embodiment of the present invention, from 0.001 to 0.1,particularly preferably from 0.005 to 0.01, equivalent, based on dieneof the formula I, of manganese compound is used.

In another embodiment of the present invention, form 0.00001 to 0.001,particularly preferably from 0.0001 to 0.0005, equivalent, based ondiene of the formula I, of manganese compound is used.

In an embodiment of the present invention, from 1 to 5, preferably from1.1 to 2, equivalents, based on manganese, of ligand L of the formula IIare used.

Suitable coligands are those compounds which are derived frommonocarboxylic acids, dibasic or polybasic carboxylic acids or diamines,i.e. monocarboxylic acids, dibasic or polybasic carboxylic acids anddiamines themselves and, in the case of monocarboxylic acids and dibasicor polybasic carboxylic acids, in particular their corresponding alkalimetal salts.

In an embodiment of the present invention, coligands are derived fromsuch monocarboxylic acids or dibasic or polybasic carboxylic acids whosepK_(a) or pK_(a) ¹ value in water at 25° C. is less than 7.

In an embodiment of the present invention, coligands are derived fromoxalic acid (III.1) dihydroxyfumaric acid (III.2), tartaric acid(III.3), maleic acid (III.4), squaric acid (III.5), 2-sulfobenzoic acid(III.6) and N(p-toluenesulfonyl)glycine (III.7):

Ascorbic acid is furthermore suitable.

A further very particularly preferred coligand is1,2-diaminocyclohexane, both the isomer mixture and the respective cis-and trans-isomers in enriched form being suitable.

In an embodiment of the present invention, coligands are used in theform of a mixture of monocarboxylic acids and alkali metal salt of therelevant monocarboxylic acid.

In an embodiment of the present invention, coligands are used in theform of a mixture of dibasic or polybasic carboxylic acid and alkalimetal salt of the relevant dibasic or polybasic carboxylic acid.

In an embodiment of the present invention, from 0.1 to 5 equivalents,preferably from 0.5 to 1 equivalent, based on manganese, of coligand areused.

According to the invention, diene of the formula I is reacted with atleast one peroxide, up to 4 equivalents of peroxide being used perequivalent of C—C double bond. Preferably, at least one equivalent ofperoxide is used per equivalent of C—C double bond. Preferably organicperoxides, in particular tert-butyl hydroperoxide, cumyl hydroperoxide,1,3-diisopropyl monohydroperoxide or 1-phenylethyl hydroperoxide, areused as the peroxide. Hydrogen peroxide (H₂O₂) is particularly preferredas the peroxide.

If it is desired to use hydrogen peroxide, it is employed as an aqueoussolution, for example as a 30% by weight or 50% by weight solution whosecontent of reactive H₂O₂ can be determined by known methods, for exampleby titration.

In an embodiment of the present invention, up to 3, preferably up to2.1, equivalents of peroxide are used per equivalent of C—C double bond.

Several procedures are possible for the order in which the reactants ofthe novel process are brought into contact.

In one embodiment of the present invention, ligand L of the formula IIand coligand are first mixed with diene of the formula I and peroxide,and manganese compound is then added.

In another embodiment of the present invention, ligand L of the formulaII is first mixed with coligand and diene of the formula I and manganesecompound, and peroxide is then added.

In another embodiment of the present invention, a complex compound isfirst prepared by bringing manganese compound and ligand L and coligandof the formula II into contact and is then mixed with diene of theformula I and then with peroxide.

In another embodiment of the present invention, a complex compound isfirst prepared by bringing manganese compound and ligand L of theformula II into contact and is then mixed with diene of the formula Iand coligand and then with peroxide.

In another embodiment of the present invention, a complex compound ofthe formula [LMn(μ-O)₃MnL]X is first prepared by bringing manganesecompound and ligand L of the formula II into contact and is then mixedwith diene of the formula I and coligand and then with peroxide.

In another embodiment of the present invention, a complex compound isfirst prepared by bringing manganese compound and ligand L and coligandof the formula II into contact and is then mixed with diene of theformula I and then with peroxide, peroxide being added in two portionsat a time interval of at least 2 hours.

The form in which the catalytically active species is present is notknown exactly. Without wishing to give preference to one theory, itappears conceivable that manganese is present at least from time to timein the oxidation state +IV during the catalytic reaction. Furthermore,it appears possible that singly or multiply μ-oxo-bridged species arepresent at least from time to time during the catalytic reaction.

In an embodiment of the present invention, the novel process is carriedout in a solvent or a mixture of solvents. Solvents used may be organicor inorganic liquids which are liquid at room temperature and, under theconditions, react only in negligible proportions, if at all, with thereactants and product, i.e. for example bisepoxide.

For example, C₁-C₄-alkanols, such as methanol, ethanol, n-propanol orisopropanol, and furthermore ketones, for example acetone, methyl ethylketone and methyl isobutyl ketone (MIBK), acetonitrile, halogenatedhydrocarbon, for example methylene chloride, chloroform or1,1,2,2-tetrachloroethane, and water are suitable. Mixtures of water andacetonitrile, mixtures of water and methanol and mixtures of water andacetone are particularly suitable.

In an embodiment of the present invention, a solvent or mixture ofsolvents is used in an amount such that the concentration of bisepoxidedoes not exceed 50% by weight and is preferably from 5 to 15% by weight.

In an embodiment of the present invention, the novel process is carriedout without having immobilized the catalyst beforehand on one or moresolid support materials, for example silica gel or alumina.

In an embodiment of the present invention, the novel process is carriedout at temperatures in the range from −50 to 100° C., preferably from−30 to 80° C., particularly preferably from −10 to 60° C. and veryparticularly preferably from 0 to 5° C.

In an embodiment of the present invention, the novel process is carriedout under a pressure in the range from 1 to 200, preferably from 1 to100, bar, particularly preferably at from atmospheric pressure to 10bar.

In an embodiment of the present invention, the novel process is carriedout at a pH of from 1 to 7, preferably from 3 to 5.

In an embodiment of the present invention, the duration of the reactionis from 1 minute to 24 hours, preferably from 30 minutes to 20 hours.

Suitable reaction vessels for carrying out the novel process are inprinciple all conventional reaction vessels, for example tubularreactors and stirred kettles, it being possible to operate stirredkettles batchwise or continuously and tubular reactors preferablycontinuously.

The novel process gives solutions of bisepoxide. The solutions ofbisepoxide which are obtainable according to the invention may comprisesmall amounts of monoepoxide, for example of the formula V.1 or V.2

the amount of monoepoxide being, as a rule, less than 8 mol %, based onpure bisepoxide. Bisepoxide can be isolated from the solutionsobtainable according to the invention and can be purified.

The present invention furthermore relates to a process for thepreparation of dithiol mixtures, also referred to below as noveltwo-stage process, wherein

-   (a) in a first stage, bisepoxide is prepared by a process as    described above and-   (b) is reacted with H₂S in the presence of at least one basic    catalyst without isolation of bisepoxide prepared in stage (a).

In an embodiment of the present invention, solutions of bisepoxideswhich are obtainable by a process described above are used, andisolation and purification operations are dispensed with.

In an embodiment, reaction is effected in stage (b) with from 1 to 10,preferably from 1 to 2, equivalents, based on one equivalent of epoxidegroup, of H₂S.

Stage (b) of the novel two-stage process is carried out in the presenceof at least one basic catalyst.

Suitable basic catalysts are basic alkali metal salts and ammoniumsalts, for example alkali metal hydroxides, alkali metal carbonates,alkali metal hydrogen sulfides and ammonium hydroxides. Examples ofalkali metal cations are Li⁺, Na⁺, K⁺, Rb⁺ and Cs⁺, in particular Na⁺and K⁺.

Examples of ammonium ions are not only unsubstituted NH₄ ⁺ but alsomonoalkylated and up to tetraalkylated ammonium, for exampleN(R⁴)(R⁵)(R⁶)(R⁷)⁺, where R⁴ to R⁷ are in each case identical ordifferent and are selected from hydrogen, benzyl, C₁-C₁₂-alkyl, such asmethyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl,tert-butyl, n-pentyl, isopentyl, sec-pentyl, neopentyl,1,2-dimethylpropyl, isoamyl, n-hexyl, isohexyl, sec-hexyl or n-decyl,particularly preferably C₁-C₄-alkyl, such as methyl, ethyl, n-propyl,isopropyl, n-butyl, isobutyl, sec-butyl and tert-butyl, phenyl orCH₂—CH₂—OH. Examples are tetramethylammonium, tetraethylammonium,benzyltrimethylammonium, methyldiethanolammonium andn-butyldiethanolammonium.

At least one basic catalyst in stage (b) is preferably selected fromalkali metal hydrogen sulfide, alkali metal hydroxide andbenzyltri(C₁-C₁₀-alkyl)ammonium hydroxide, and sodium hydrogen sulfide,potassium hydrogen sulfide, sodium hydroxide, potassium hydroxide andbenzyltrimethylammonium hydroxide are very particularly preferred.

In an embodiment of the present invention, from 10⁻⁴ to 10, preferablyfrom 0.5 to 5, % by weight, based on bisepoxide, of basic catalyst areused.

In an embodiment of the present invention, stage (b) is carried out at apressure in the range from 1 to 200, preferably from 1 to 100,particularly preferably from 1 to 10, bar.

In an embodiment of the present invention, stage (b) is carried out at atemperature in the range from −50 to 100° C., preferably from −30 to 80°C., particularly from −10 to 60° C., very particularly preferably from15 to 35° C.

In an embodiment of the present invention, the novel process is carriedout at a pH of from 8 to 13, preferably from 9 to 11.

In an embodiment of the present invention, a bisepoxide solutionobtainable after stage (a) of the novel process is used as a startingmaterial, H₂S is added, at least one basic catalyst is then added andthe reaction is allowed to proceed.

In an embodiment of the present invention, further solvent selected fromthe solvents mentioned above under stage (a) can be added in stage (b)of the novel two-stage process.

In an embodiment of the present invention, the duration of reaction isfrom 10 minutes to 4 hours, preferably from 0.5 hour to 2 hours.

In principle, all conventional reaction vessels are suitable as reactionvessels for carrying out the novel two-stage process, for exampletubular reactors and stirred kettles, it being possible to operatestirred kettles batchwise or continuously and tubular reactorspreferably continuously. Continuously operated stirred kettle cascadesare also conceivable as suitable vessels.

Without wishing to give preference to one theory, it appears conceivablethat unreacted peroxide from stage (a) is trapped by any excess H₂S instage (b).

By carrying out the novel two-stage process, solutions of dithiolmixtures or corresponding salts of dithiols, to which the presentinvention likewise relates, are obtained. From novel solutions ofdithiol mixtures, it is possible to isolate dithiol mixtures or theircorresponding salts by methods known per se, for example neutralizationor distilling off the solvent or solvents. In order to obtainparticularly pure dithiol mixtures, distillation can be effected, forexample under reduced pressure.

Via methods known per se, for example chromatography, dithiol mixturesobtainable by the novel process can be separated into erythro- andthreo-dithiol, and the enantiomers of threo-dithiol can be separated orincreased in concentration by chiral discrimination.

The present invention furthermore relates to dithiol mixtures comprising

-   -   (A) from 55 to 65, preferably from 59 to 61, mol % of        erythro-dithiol and    -   (B) from 35 to 45, preferably from 39 to 41, mol % of        threo-dithiol of the formula IV

where the variables are defined as above, and corresponding salts ofnovel dithiol mixtures.

Novel dithiol mixtures comprise compounds which can be represented inFischer projection as follows:

Novel dithiol mixtures may comprise corresponding salts of erythro-IVand threo-IV.

In an embodiment of the present invention, threo-IV is present in theform of a racemate.

In an embodiment of the present invention, where R¹ is selected fromunsubstituted or substituted C₁-C₁₂-alkyl, erythro-IV is present in theform of a racemate.

Novel dithiol mixtures may be contaminated with small amounts ofhydroxythiol of the formulae VI.1 or VI.2

the amount of hydroxythiol generally not exceeding 8 mol %, based onpure dithiol or corresponding salt of dithiol of the formula IV.

Examples of corresponding salts are in particular the mono- and disodiumsalts, mono- and dipotassium salts and potassium sodium salts ofdithiols of the formula IV, and furthermore the corresponding calciumand magnesium salts. The ammonium salts and primary, secondary, tertiaryand in particular quaternary mono- and diammonium salts should also bementioned.

Preferred mono- and diammonium salts have, as cations, those of theformula N(R³)(R⁴)(R⁶)(R⁶)⁺, where R³ to R⁶ in each case are identical ordifferent and are selected from hydrogen, C₁-C₁₂-alkyl, phenyl orCH₂—CH₂—OH. Examples are tetramethylammonium, tetraethylammonium,methyldiethanolammonium and n-butyldiethanolammonium.

The present invention furthermore relates to aqueous solutionscomprising novel dithiol mixture. Novel aqueous solutions can beobtained, for example, by dissolving novel dithiol mixture orcorresponding salt in water. Novel aqueous solutions preferably have asolids content of from 0.1 to 50% by weight.

It has now been found that novel dithiol mixtures and theircorresponding salts, for example in the form of their aqueous solution,can be used in an excellent manner for the treatment of hides of deadanimals.

The present invention therefore relates to the use of novel dithiolmixtures for the treatment of hides of dead animals.

The present invention furthermore relates to a process for removinghorny substances from hides of dead animals using at least one noveldithiol mixture, also referred to below as novel treatment process.

In the context of the present invention, horny substances are understoodas meaning calluses, feathers, nail and claw parts and in particularhairs of animals.

Hides of dead animals may still comprise residues of flesh of therelevant dead animals. What is essential to the invention, however, isthat they comprise horny substances. The amount of horny substance,based on the total weight of the hide or of the skin or of the skin fur,is not critical. The novel process is suitable both for removing largeamounts of horny substance and, for example, for removing small hairresidues.

In the context of the present invention, dead animals are understood asmeaning not only slaughtered animals or animals killed in another mannerbut also those animals which have died as a result of accidents, forexample traffic accidents or fights with members of their own species orother animals, or through natural causes, such as age or disease.

The hides of dead animals are usually hides of cattle, calves, pigs,goats, sheep, lambs, elks, game, for example stags or roe deer, andfurthermore birds, for example ostriches, fish or reptiles, for examplesnakes.

For carrying out the novel treatment process, it is advantageous toproceed as follows.

At least one novel dithiol mixture is added to at least one hide or hideparts of at least one dead animal.

In general, an amount of from 0.1 to 5% by weight, based on the hideweight or salted weight of the hides, of at least one novel dithiolmixture is sufficient. From 0.5 to 2.5% by weight are preferred and from0.75 to 1.5% by weight are particularly preferred.

The novel treatment of the hides with at least one novel dithiol mixtureis preferably effected during liming or during painting, in particularunder hair-destroying or under hair-preserving conditions. During limingor during painting, it is possible to manage with a concentration ofless than 1% by weight of Na₂S or NaHS instead of the usualconcentration of about 4% by weight of Na₂S or NaHS or even slightlymore, with an equivalent or even better effect with regard to theremoval of horny substances.

In a variant of the novel process, during the liming, at least one noveldithiol mixture is used together with thiols known from tanning, forexample mercaptoethanol or thioglycolic acid. Preferably, less than 0.5%by weight of mercaptoethanol or thioglycolic acid is used.

In a very particularly preferred variant of the novel process, however,it is possible to dispense with the use of Na₂S or NaHS or otherfoul-smelling sulfur-containing reagents.

In an embodiment of the present invention, hides are treated in anaqueous liquor. The liquor ratio may be from 1:10 to 10:1, preferablyfrom 1:2 to 4:1, particularly preferably up to 3:1, based on the hideweight or salted weight of the hides.

In an embodiment of the present invention, the novel treatment processcan be carried out at a pH of from 7 to 14, preferably from 8 to 13,particularly preferably from 9 to 12.5.

For establishing the pH, it is possible to add up to 3% by weight, basedon the liquor, of lime (including slaked lime). However, the amount oflime can also be substantially reduced. In a preferred variant of thenovel treatment process, the use of lime is dispensed with. In thepreferred embodiment, one or more inorganic basic alkali metal compoundsare added, for example one or more hydroxides or carbonates of alkalimetals, preferably of sodium or potassium, very particularly preferablyof sodium. Other suitable inorganic basic alkali metal compounds arealkali metal silicates. It is also possible to add basic amines, forexample ammonia, methylamine, dimethylamine, ethylamine ortriethylamine, or combinations of alkali metal compound and one or morebasic amines.

In addition to water, further organic solvents may also be present inthe liquor, for example up to 20% by volume of ethanol or isopropanol.

The novel treatment process can be carried out in vessels which arecustomary in tanning and in which liming is usually effected.Preferably, the novel treatment process is carried out in rotatabledrums having internals. The speed is usually from 0.5 to 100, preferablyfrom 1.5 to 10, particularly preferably up to 4.5, rpm.

The pressure and temperature conditions for carrying out the noveltreatment process are generally not critical. The procedure atatmospheric pressure has proven suitable; pressure increased to 10 baris likewise conceivable. Suitable temperatures are from 10 to 45° C.,preferably from 15 to 35° C., particularly preferably from 25 to 30° C.

At least one novel dithiol mixture can be metered at the beginning ofthe novel treatment process, but it is also possible first to soak thehides under basic conditions and to meter at least one novel dithiolmixture only after some time. The metering can be effected in one step,i.e. the total amount of novel dithiol mixture is metered in one step;however, novel dithiol mixtures can also be metered in portions orcontinuously.

The novel treatment process can be carried out in a period of from 10minutes to 48 hours, preferably from 1 to 36, particularly preferablyfrom 3 to 15, hours.

Of course, assistants customary in turning may also be added forcarrying out the novel treatment process, for example phosphines, e.g.triphenylphosphine or tris(2-carboxyethyl)phosphine hydrochloride, andfurthermore hydroxylamine, urea, guanidine or guanidinium hydrochloride,hydrazine, biocides, enzymes, surfactants and emulsifiers.

Unhaired pelts can be produced in an excellent manner by means of thenovel treatment process. Surprisingly, it is also found that theepidermis is completely or at least substantially detached after a shorttreatment time.

It was furthermore found that pelts produced by the novel treatmentprocess are very suitable for the production of leather. After furtherprocessing, in a manner customary in the tannery, of pelts produced bythe novel treatment process, i.e. bating, if appropriate deliming,pickling, chromium-free tanning or chrome tanning, retaining andfinishing, it is observed that pelts produced by the novel treatmentprocess can be further processed to give leather having an improvedyield per unit area and less damage due to swelling compared withleather which is produced from pelts which were unhaired with the aidof, for example, Na₂S, NaHS, thioglycolic acid or aminoethanol.

The working examples which follow illustrate the invention.

-   1 Preparation of a mixture of 40 mol % of    erythro-1,4-dimercaptobutane-2,3-diol and 60 mol % of racemic    threo-1,4-dimercaptobutane-2,3-diol

(a) Preparation of Bisepoxide

(a.1)

The following were mixed with one another in a 150 ml glass autoclavehaving an inlet tube:

42.6 g of acetonitrile,9 ml of aqueous manganese(II) acetate solution having a concentration of0.02 mol of Mn/l,9 ml of 1,4,7-trimethyl-1,4,7-triazacyclononane having a concentrationof 0.03 mol/l,9 ml of aqueous sodium oxalate/oxalic acid buffer (molar ratio: 1:1)having a concentration of 0.06 mol/l of the sum of oxalate and oxalicacid.

The solution thus obtainable was cooled to about −40° C. with the aid ofa dry ice/acetone bath. 3.34 g (61.8 mmol) of 1,3-butadiene were thencondensed. A temperature of 0° C. was then established with the aid ofan ice bath. 16.7 g of 50% by weight aqueous H₂O₂ solution (246 mmol ofH₂O₂) were then pumped in in the course of 1 hour, it being ensured thatthe temperature did not increase above 25° C. It was observed that thepressure in the autoclave increased to 5.2 bar. Thereafter, the ice bathwas removed and stirring was continued for 2 hours at room temperature.Thereafter, a pressure of 3.2 bar was found to have been established.

16.6 g of 50% by weight aqueous H₂O₂ solution (244 mmol of H₂O₂) werethen pumped in, it being ensured that the temperature did not increaseabove 25° C. It was observed that the pressure in the autoclaveincreased to 3.8 bar. Thereafter, the ice bath was removed and stirringwas effected for 5.5 hours at room temperature. After 5.5 hours, it wasfound that a pressure of 5 bar had been established.

The pressure was then let down and the composition of the resulting palesolution (94.6 g) was determined by gas chromatography. A content of58.4 mmol of bisepoxide of the formula VII.1 and 3.4 mmol ofvinyloxirane IV.1.1

was determined. The yield of desired bisepoxide VII.1 was 95.5%.(a.2)

The reaction from (a.1) was repeated, but stirring was effected for 12hours at room temperature after pumping in 16.7 g of 50% by weightaqueous H₂O₂ solution and removing the ice bath. Further processing wasthen effected as described under (a.1). Bisepoxide VII.1 was obtained invery good yield.

(b) Preparation of Novel Dithiol Mixture

50 g of the solution resulting from 1 (a.1) were initially taken in a400 ml glass autoclave and 6 bar H₂S was forced in at room temperature.A solution of 1.04 g of NaOH (solid) in 20 ml of methanol was added withthe aid of an HPLC pump. During the addition of methanol/NaOH, atemperature increase from 25 to 35° C. was observed.

The pressure was kept at 6 bar by continuously forcing in H₂S. The linesof the HPLC pump were then flushed with 50 ml of acetonitril.

By the end of the reaction, which was evident from a decline in thetemperature, the pressure in the autoclave was let down and theautoclave was freed from excess H₂S over a period of 14 hours by passingN₂ through the reaction mixture.

83.8 g of a clear solution of dithiol mixture were obtained. The noveldithiol mixture IV.1 obtained was separated by gas chromatography and,according to gas chromatography, had the following composition:

40 mol % of erythro-IV.160 mol % of threo-IV.1 in the form of a racemate.Conditions for the gas chromatography: column: HP-5, length: 30 m,internal diameter=0.25 mm, film thickness 0.25 μm, detector: WLD, Init.T.: 40° C., Init. time: 5 min, rate: 10° C./min, final temperature 290°C., retention time IV.1: 18.00-18.50 min.

-   2. Treatment of Pelts with Novel Dithiol Mixture

The values in % by weight are based in each case on the salted weight,unless stated otherwise.

General Pretreatment:

A southern German cattle hide was first presoaked at 28° C. with 200% byweight of water and 0.2% by weight of C₁₅H₃₁—O—(CH₂—CH₂—O)₇—H for 10minutes in a drum with gentle stirring. The liquor was discharged andsoaking was then effected with 100% by weight of water, 0.2% by weightof C₁₅H₃₁—O—(CH₂—CH₂—O)₇—H and 0.5% by weight of Na₂CO₃ with occasionalstirring for 19 hours. The liquor was then discharged.

The softened southern German cattle hides were fleshed in the greenstate (thickness about 4 mm) and the butts of the hides were cut intohide pieces of 2.5 kg green weight each.

Below, the values in % by weight are based in each case on the greenweight, unless stated otherwise.

-   2.1. Liming of Comparative Example C1

For comparative example C1, 100% by weight, based on green weight, weretreated in a rotatable 10 l drum having internal baffles in successionwith 60 parts by weight of water, 0.8% by weight of NaSH and 3% byweight of slaked lime. 0.75% by weight of sodium sulfide followed at 30minute intervals. The drum was operated for a further 45 minutes at 15revolutions per minute. A further 40 parts by weight of water were thenmetered. After 10 hours at from 23 to 27° C. and 5 revolutions perminute, the experiments were terminated by discharging the liquor andthe hides were washed twice for 15 minutes with 150 parts by weight ofwater.

-   2.2. Hair-Destroying Liming of the Novel Examples 2.1 to 2.4

In the novel examples 2.1 to 2.4, first 60% by weight of water wereadded to 100% by weight, based on green weight, in rotatable 10 l drumshaving internal baffles, and treatment with products, as evident fromtable 1, was then effected.

TABLE 1 Amount used Time Example [% by weight] Product [min] 2.1 0.5Sodium sulfhydrate (70%) 0.5 Dithiol mixture IV.1 60 1.2 Slaked lime 601.2 Slaked lime 60 2.2 1.0 Dithiol mixture IV.1 60 1.2 Slaked lime 601.2 Slaked lime 2.3 1.5 Dithiol mixture IV.1 60 1.2 Slaked lime 60 1.2Slaked lime 60 2.4 1.0 Dithiol mixture IV.1 60 1.0 Aqueous sodiumhydroxide solution 30 (50% by weight) 1.0 Aqueous sodium hydroxidesolution 30 (50% by weight) 50 Water 0.4 Aqueous sodium hydroxidesolution 60 (50% by weight) 50 Water 30

The drums were operated for a further 45 minutes at 5 revolutions perminute. A further 40% by weight of water were then metered. After 10hours at from 23 to 27° C. with periodic operation at 3 revolutions perminute over 5 minutes per hour in each case, the experiments wereterminated by discharging the liquors, and the pelts obtained werewashed twice for 15 minutes each time with 150% by weight of water.

-   2.3. Assessment of Pelts According to Comparative Example and    According to Novel Examples after Liming

The pelts treated according to the novel examples were only slightlysuperior to the hides treated according to comparative example C1 withrespect to the swelling but were distinguished by a smoother and flattergrain, in particular the pelts of novel examples 2.3 and 2.4. Theepidermis and the hairs with hair root in the pelts according toexamples 2.1 to 2.3 had been substantially destroyed and those in peltsaccording to example 2.4 had been completely destroyed.

1. A process for the preparation of a bisepoxide, comprising: reactingat least one conjugated diene of formula I

where R¹ is selected from the group consisting of hydrogen, anunsubstituted C₁-C₁₂-alkyl, and a C₁-C₁₂-alkyl substituted by one ormore S—H or O—H groups, with at least one peroxide in the presence of acatalyst, said catalyst obtained by a process comprising contacting atleast one manganese compound selected from the group consisting ofA₂MnX₄, AMnX₃, MnY, MnX₂ and MnX₃ with at least one ligand L of formulaII

where X₂, X₃, and X₄ are each a monovalent anion, Y is a divalent anion,A is selected from the group consisting of an alkali metal ammonium, andan alkylated ammonium, R² are each different or identical and areC₁-C₂₀-alkyl, and at least one coligand of a monocarboxylic acid, adibasic carboxylic acid, a polybasic carboxylic acid, or a diamine,wherein up to 4 equivalents of peroxide are present per equivalent ofC—C double bond.
 2. The process according to claim 1, which is carriedout in the presence of at least one solvent.
 3. The process according toclaim 1, wherein said at least one coligand is oxalate.
 4. A process forthe preparation of dithiol mixtures, comprising: reacting a bisepoxideobtained by the process according to claim 1 with H₂S in the presence ofat least one basic catalyst.
 5. The process according to claim 4,wherein said at least one basic catalyst is at least one member selectedfrom the group consisting of alkali metal hydrogen sulfide, alkali metalhydroxide and benzyltri(C₁-C₁₀-alkyl)ammonium hydroxide. 6-10.(canceled)
 11. The process according to claim 1, wherein R¹ is hydrogen.12. The process according to claim 1, wherein said at least one coligandis at least one isomer of 1,2-diaminocyclohexane.
 13. The processaccording to claim 1, wherein said at least one manganese compound is atleast one selected member from the group consisting of manganese(II)sulfate, MnSO₄.H₂O, manganese(II) acetate, Mn(OAc)₂.4H₂O, manganese(II)chloride, MnCl₂.4H₂O, manganese(II) perchlorate, Mn(ClO₄)₂.6H₂O andpotassium hexachloromanganate(IV).
 14. The process according to claim 1,wherein said at least one manganese compound is present in an amount offrom 0.001 to 0.1 equivalents, based on the amount of said at least oneconjugated diene of formula I.
 15. The process according to claim 1,wherein said at least one manganese compound is present in an amount offrom 0.005 to 0.1 equivalents, based on the amount of said at least oneconjugated diene of formula I.
 16. The process according to claim 1,wherein said at least one manganese compound is present in an amount offrom 0.00001 to 0.001 equivalents, based on the amount of said at leastone conjugated diene of formula I.
 17. The process according to claim 1,wherein said at least one manganese compound is present in an amount offrom 0.00001 to 0.0005 equivalents, based on the amount of said at leastone conjugated diene of formula I.
 18. The process according to claim 1,wherein said at least one ligand of formula II is present in an amountof from 1 to 5 equivalents based on the amount of manganese.
 19. Theprocess according to claim 1, wherein said at least one ligand offormula II is present in an amount of from 1.1 to 2 equivalents based onthe amount of manganese.
 20. The process according to claim 1, whereinsaid at least one peroxide is at least one member selected from thegroup consisting of tert-butyl hydroperoxide, cumyl hydroperoxide,1,3-diisopropyl monohydroperoixde, 1-phenylethyl hydroperoxide, andhydrogen peroxide.
 21. The process according to claim 1, occurring at atemperature of from −50 to 100° C.
 22. The process according to claim 1,occurring at a pressure of from 1 to 200 bar.
 23. The process accordingto claim 1, occurring at a pH of from 1 to
 7. 24. The process accordingto claim 1, wherein said bisepoxide is the bisepoxide of formula VII.1:


25. The process according to claim 1, wherein at least one equivalent ofperoxide is present per equivalent of C—C double bond.